1. Field of the Invention
The present invention relates to gauges and more particularly to a liquid helium level indicating gauge to indicate the level of liquid helium in a container.
2. Description of the Prior Art
In the conventional level gauge for liquid helium, a superconductive wire of Nb-Ti (niobium titanium) alloy has been employed as the element for the liquid level detection. However, the gauge has the following disadvantages.
(1) Since the superconductivity transition temperature (Tc) of the superconductive Nb-Ti wire is too high for the temperature of liquid helium, the part of the wire just above the liquid level too easily enters into a superconductive state. To make this part normally conductive, it is necessary for it to be heated with Joule heat by using an electric current (about 70 mA). The heating consumes a relatively large quantity liquid helium (about 0.02 l/hour).
(2) Since the Nb-Ti wire has a low electric resistance even in the normally conductive state, the wire diameter is required to be reduced (to about 0.2 .0. mm) for improvement in the measuring sensitivity. Such a fine wire has a low mechanical strength and is particularly susceptible to shocks.